1. Field of the Invention
The present invention relates to a method of forming a sintered object of a predetermined shape by stacking a plurality of sintered layers (hardened layers) each formed by irradiating a layer of inorganic or organic powdery material with an optical sintering beam.
2. Description of the Related Art
This sort of the sintered object forming method is disclosed in, for example, Japanese Laid-open Patent Publication No. 2000-73108. According to this publication, the three-dimensional sintered object is formed by depositing a layer of powdery metallic material on a predetermined site, directing an optical sintering beam to the layer of the powdery metallic material to form a sintered layer, forming another one or more sintered layers on the underlying sintered layer by repeating the depositing step and the beam directing step a number of times equal to the number of the sintered layers desired to be formed. The resultant sintered layers are mechanically interlocked with each other.
In this known method, a laminated body M of a size larger by a predetermined quantity than the eventually formed sintered object, each consisting of a predetermined number of the sintered layers, is formed as shown in FIG. 20A, followed by trimming the resultant laminated body M with the use of a machining tool 3 such as a ball end mill to remove an unwanted surface area or any other unwanted portion from around the laminated body M as shown in FIG. 20B. Thus, each time the laminated body is formed, the trimming is effected to remove the unwanted surface area or any other unwanted portion from around such laminated body.
Since when upon completion of the trimming process a new laminated body is to be formed above the underlying laminated body M, irradiation with the optical sintering beam L is effected so that the subsequently formed laminated body can have a size larger by a predetermined quantity than the underlying laminated body M, an excessively sintered growth M1 tends to be formed as a result of application of laser energy to form a sintered layer, which forms the lowermost one of a plurality of sintered layers of a laminated body, immediately above the uppermost one of a plurality of sintered layers of the underlying laminated body as shown in FIG. 21C. This excessively sintered growth M1 generally represents a shape similar to the shape of icicles and results from an excessive portion of the powdery metallic material having been sintered.
However, it has been found that since in the prior art method a zone A to be removed and a zone B in which each laminated body is formed, that is, a zone of the laminated body are set to exactly align with each other, that is, to lie in the same zone, a trimming path designed to encompass such zone A to be removed will not reach down to the site where the excessively sintered growth M has been formed. Accordingly, as shown in FIG. 20D, the excessively sintered growth M1 tends to be left unremoved, making it difficult to finish the three-dimensional sintered object having a smooth surface.
Also, since as shown in FIGS. 21A and 21B, the trimming step is carried out to the laminated body N after the layers of the powdery material have been sintered successively to complete the laminated body N and the trimming step is similarly carried out to the laminated body N+1 after the layers of the powdery material have been sintered successively to complete the laminated body N+1 above the laminated body N, one or some of the sintered layers of the laminated body N immediately below the laminated body N+1 are already trimmed at the time the lowermost sintered layer of the laminated body N+1 has been formed as shown in FIG. 21C. Accordingly, when the laminated body N+1 is formed, the necessity arises to create a CAD (computer aided design) data for implementing sintering of the powdery material at a portion B of the laminated body N removed by trimming. In addition, considering that a partially or incompletely sintered layer is left during sintering of the sintered layer M1 at a location immediately below the sintered layer M1 of the laminated body N+1 and this laminated body N+1 lies outside the zone to be trimmed, the sintered layer M1 remains on the eventually formed object even after completion of formation of the laminated body N+1.
In FIGS. 21A to 21C, reference character H represents the thickness of each sintered layer, reference character Hz represents an area to be removed by trimming, reference character A represents a zone to be trimmed of the laminated body N, reference character S represents a contour of the sintered layer to be formed, and reference character Sf represents a contour of a final cross-sectional shape of the eventually formed object.
FIG. 22 illustrates conceptually a relation in dimension between the contour S of the sintered layer and the final contour Sf of the cross-sectional shape of the eventually formed sintered object 1.